1. Field of Invention
The present invention relates to a display, and more particularly to a source driving circuit in the display.
2. Description of Related Art
Various types of electronic devices have display devices, such as TVs, laptop computers, monitors and mobile communication terminals. The display devices are requested to be thin and/or light in order to save the volume and the cost of the electronic devices. To satisfy these requirements, various Flat Panel Displays (FPDs) have been developed as alternatives to more conventional cathode ray tube displays. A Liquid Crystal Display (LCD) is one kind of Flat Panel Display. The LCD device includes a timing controller, a gate driver, a display panel and a source driver.
Generally, digital video data are transmitted to the LCD device from an external host system, e.g., a graphic source. The video data format is converted by the timing controller of the LCD device, and transmitted to the source driver of the LCD device. In addition, the timing controller generates various control signals to the source driver and the gate driver for controlling the source driver and the gate driver to operate. Under the control of the control signals, the gate driver sequentially drives each gate line and then the source driver transmits the video data to the pixels on each gate line via the data lines for displaying the image.
FIG. 1 shows a block diagram of a conventional source driver. Referring to FIG. 1, the source driver 100 includes a shift register 110, a level shifter 120, a digital-to-analog converter 130 and an output buffer 140. The shift register 110 stores the video data in response to the horizontal synchronization signal (not shown in FIG. 1). Since the shift register 110 and the digital-to-analog converter 130 respectively operate at different voltage level, the level shifter 120 transforms the voltage level of the outputs of the shift register 110 to fit in with the voltage level of the digital-to-analog converter 130. The digital-to-analog converter 130 converts the digital video data into the analog signals and the output buffer 140 enhances the driving ability of the analog signals for driving the pixels on display panel.
The level shifter plays an important role in the source driver. However, the transition state of the level shifter may trigger the digital-to-analog converter 130 to output inaccurate voltage to the display panel. Under some circumstances, the inaccurate voltage outputted while the level shifter is in transition state may be considerably different to the voltage outputted while the level shifter is in normal state. In the meanwhile, the voltage outputted by the digital-to-analog converter 130 changes dramatically, and thus a large current is induced. The unexpected situation may cause the abnormal operation of the source driver. Therefore, it is desirable to design a proper level shifter to solve the said problem.